please please help..when did i get pregnant

i had my period late in jan..it only lasted a few days and was alot lighter than normal...then i had intercourse 3 days after it ended..3 days after intercourse i had a pinching pain in the lower part of my abdomen on the side..could that possibly been implantation i was feeling..and is it even possible to ovulate a few days after your period..my period usually starts around the 6-8th and it started the 10....i took a test on the 30 and it was negative ..then i took another one on the night of the 1st.and it was positive..i had sex on the 18th and the 24th..i felt the pinching on the 21st..trying to figure out which time i possibly concieved